Method and apparatus for inter-cell interference coordination in a wireless communication system

ABSTRACT

A method of performing interference management by a base station (BS) in a wireless communication system. The BS receives, from another BS, an interference management message including a silenced subframe pattern of the another BS. The BS transmits, to a user equipment (UE), a radio resource configuration (RRC) message including subframe set information for interference measurement, and receives, from the UE, channel state information (CSI) feedback including a result of the interference measurement. The subframe set information is configured based on the silenced subframe pattern of the another BS, and the subframe set information restricts the interference measurement of the UE to specific subframes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation application of U.S. application Ser.No. 14/754,338 filed on Jun. 29, 2015, which is a Continuationapplication of U.S. application Ser. No. 13/980,243 filed on Jul. 17,2013 (now U.S. Pat. No. 9,088,394 issued on Jul. 21, 2013), which is aNational Stage of PCT/KR2012/000641 filed on Feb. 3, 2012, which claimsthe benefit of U.S. Provisional Application No. 61/439,923 filed on Feb.6, 2011, 61/441,255 filed on Feb. 9, 2011, and 61/445,000 filed on Feb.21, 2011. The entire contents of all of these applications are herebyincorporated by reference.

BACKGROUND OF THE INVENTION

A following description relates to a wireless communication system, andmore particularly, to a method of performing inter-cell interferencecoordination in a wireless communication and apparatus therefor.

FIG. 1 is a diagram of a heterogeneous network wireless communicationsystem 100 including a macro base station and a micro base station. Inthis specification, a terminology of a heterogeneous network means anetwork in which the macro base station 110 and micro base stations121/122 co-exist although an identical Radio Access Technology (RAT) isused.

The macro base station 110 means a general base station of a wirelesscommunication system having a wide coverage and high transmit power. Themacro base station may be called a macro cell.

For instance, the micro base station 121/122 can be called a micro cell,a pico cell, a femto cell, a home eNB (HeNB), a relay, or the like. Themicro base station 121/122 is a small version of the macro base station110 and can operate independently in a manner of performing most offunctions of the macro base station. The micro base station is sort of abase station installed (overlay) in an area covered by the macro basestation or the base station installable (non-overlay) in a radio shadowarea where the macro base station is not able to cover. Compared to themacro base station 110, the micro base station 121/122 can accommodatesmall numbers of user equipments with a narrower coverage and lowertransmit power.

A user equipment 131 can be directly served from the macro base station110 (hereinafter a macro UE) and a user equipment 132 can be served fromthe micro base station 122 as well (hereinafter a micro UE). In somecases, the user equipment 132 existing in the coverage of the micro basestation 122 may be served from the macro base station 110.

According to whether an access restriction is applied to a userequipment, the micro base station can be classified into two types. Afirst type corresponds to a Closed Subscriber Group (CSG) micro basestation and a second type corresponds to an Open Access (OA) or an OpenSubscriber Group (OSC) micro base station. The CSG micro base stationcan serve permitted specific user equipments and the OSG micro basestation can serve all user equipments without any separate accessrestriction.

SUMMARY OF THE INVENTION

In the aforementioned heterogeneous network, if a user equipment servedby the macro base station is adjacent to the micro base station,interference can occur in a downlink signal received by the macro UEfrom the macro base station due to a strong downlink signal from themicro base station. Or, the user equipment served by the micro basestation can be strongly interfered by the downlink signal of the macrobase station. As mentioned earlier, if one cell is strongly interferedby a neighboring cell, the neighboring cell may perform an Inter-CellInterference Coordination (ICIC) to reduce/eliminate interference in amanner of restricting the transmission of the neighboring cell in a partof resource region (e.g., a part of subframe).

The ICIC can be performed in a time resource or a frequency resource.For instance, one cell can inform a neighboring cell(s) of a size ofdownlink/uplink interference (or transmit power) on a specific frequencydomain. Or, one cell can inform the neighboring cell(s) of the timedomain where the cell does not perform a downlink/uplink scheduling.According to a legacy scheme, the ICIC on the frequency resource isdefined that the ICIC is applied without a decision on the time resource(i.e., all time resources) and the ICIC in the time resource is definedthat the ICIC is applied without a decision on the frequency resource(i.e., all frequency resources). Hence, if both the ICIC in the timeresource and the ICIC on the frequency resource are simultaneouslyapplied, there may exist a problem of not capable of specifying the timeand frequency resource to which the ICIC is applied.

A technical task of the present invention is to provide a method ofenabling an ICIC operation to be correctly and efficiently performed ina manner of clearly specifying a resource position to which the ICIC isapplied by determining whether frequency resource ICIC information isapplied based on time resource ICIC information, even in case that theICIC in the time resource and the ICIC on the frequency resource arecoexist.

Technical tasks obtainable from the present invention are non-limitedthe above-mentioned technical task. And, other unmentioned technicaltasks can be clearly understood from the following description by thosehaving ordinary skill in the technical field to which the presentinvention pertains.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, accordingto one embodiment of the present invention, a method of performing aninter-cell interference coordination (ICIC) in a wireless communicationsystem includes the steps of receiving a time domain ICIC information ofa first cell and a frequency domain ICIC information of the first cellfrom the first cell by a second cell, assuming validity of the frequencydomain ICIC information of the first cell based on the time domain ICICinformation of the first cell by the second cell, and performing anuplink or a downlink scheduling by the second cell based on a result ofthe assuming step.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, accordingto a different embodiment of the present invention, a method ofperforming an inter-cell interference coordination (ICIC) in a wirelesscommunication system includes the steps of transmitting a time domainICIC information of a first cell and a frequency domain ICIC informationof the first cell to a second cell by the first cell, predicting aresult of assumption performed by the second cell for validity of thefrequency domain ICIC information of the first cell based on the timedomain ICIC information of the first cell, and performing an uplink or adownlink scheduling by the first cell based on the result of prediction.

In order to solve the aforementioned technical task, according to adifferent embodiment of the present invention, a base station of asecond cell performing an inter-cell interference coordination (ICIC) ina wireless communication system includes a transceiving moduleconfigured to transmit and receive a signal with a first cell and aprocessor configured to control the base station including thetransceiving module, the processor configured to receive a time domainICIC information of the first cell and a frequency domain ICICinformation of the first cell from the first cell via the transceivingmodule, the processor configured to assume validity of the frequencydomain ICIC information of the first cell based on the time domain ICICinformation of the first cell, the processor configured to perform anuplink or a downlink scheduling of the second cell based on a result ofthe assumption.

In order to solve the aforementioned technical task, according to afurther different embodiment of the present invention, a base station ofa first cell performing an inter-cell interference coordination (ICIC)in a wireless communication system includes a transceiving moduleconfigured to transmit and receive a signal with a second cell and aprocessor configured to control the base station including thetransceiving module, the processor configured to transmit a time domainICIC information of the first cell and a frequency domain ICICinformation of the first cell to the second cell via the transceivingmodule, the processor configured to predict a result of assumption ofthe second cell for validity of the frequency domain ICIC information ofthe first cell based on the time domain ICIC information of the firstcell, the processor configured to perform an uplink or a downlinkscheduling of the first cell based on a result of the prediction.

In the embodiments according to the present invention, followingdescription can be commonly applied.

The time domain ICIC information of the first cell can include a silentsubframe configuration information of the first cell.

The assuming step can include the step of assuming that the frequencydomain ICIC information of the first cell is not valid in a downlinksubframe n, which is configured as a silent subframe by the first cell.

The frequency domain ICIC information assumed to be invalid maycorrespond to an RNTP (relative narrowband transmission power) of thefirst cell.

The assuming step can include the step of assuming that the frequencydomain ICIC information of the first cell is not valid in a uplinksubframe n+k corresponding to a downlink subframe n, which is configuredas a silent subframe by the first cell.

The frequency domain ICIC information assumed to be invalid can includeat least one of an IOI (interference overhead indication) or an HII(high interference indication).

Scheduling information on an uplink transmission in the uplink subframen+k can be transmitted in the downlink subframe n.

The assuming step can include the step of assuming that the frequencydomain ICIC information of the first cell is valid in a subframe, whichis not configured as a silent subframe by the first cell.

The method can further include the step of determining a time resourceand a frequency resource used to measure interference in the second cellbased on a result of the assuming step.

The method further includes the step of receiving an informationindicating a resource region where the frequency domain ICIC informationof the first cell is valid from the first cell and wherein the assumingstep can be performed based on the information indicating the resourceregion where the frequency domain ICIC information of the first cell isvalid.

The resource region where the frequency domain ICIC information of thefirst cell is valid can be determined on a time resource and a frequencyresource.

The silent subframe may correspond to a subframe configured as an ABS(almost blank subframe) by the first cell.

The above-mentioned general description for the present invention andthe following details of the present invention may be exemplary and areprovided for the additional description for the inventions in theappended claims.

According to the present invention, a method of enabling an ICICoperation to be correctly and efficiently performed in a manner ofclearly specifying a resource position to which the ICIC is applied bydetermining whether frequency resource ICIC information is applied basedon time resource ICIC information can be provided.

Effects obtainable from the present invention may be non-limited by theabove mentioned effect. And, other unmentioned effects can be clearlyunderstood from the following description by those having ordinary skillin the technical field to which the present invention pertains.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

FIG. 1 is a diagram of a heterogeneous network wireless communicationsystem 100 including a macro base station and a micro base station;

FIG. 2, including view (a) and view (b), is a diagram for a structure ofa downlink radio frame;

FIG. 3 is a diagram for a resource grid in a downlink slot;

FIG. 4 is a diagram for a structure of a downlink subframe;

FIG. 5 is a diagram for a structure of an uplink subframe;

FIG. 6, including view (a) and view (b), is a structured diagram of aradio communication system having multiple antennas;

FIG. 7 is a flowchart showing an example of the present invention for anICIC operation in case that ICIC information on a time and frequencyresource of one cell is delivered to a different cell;

FIG. 8 is a flowchart showing an example of the present invention for anICIC operation in case that ICIC information on a time resource of onecell and the ICIC information on a frequency resource of a differentcell are exchanged with each other; and

FIG. 9 is a diagram for a configuration of a base station deviceaccording to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The embodiments in the following description may correspond tocombinations of elements and features of the present invention inprescribed forms. And, it may be able to consider that the respectiveelements or features may be selective unless they are explicitlymentioned. Each of the elements or features may be implemented in a formfailing to be combined with other elements or features. Moreover, it maybe able to implement an embodiment of the present invention by combiningelements and/or features together in part. A sequence of operationsexplained for each embodiment of the present invention may be modified.Some configurations or features of one embodiment may be included inanother embodiment or can be substituted for correspondingconfigurations or features of another embodiment.

In this specification, embodiments of the present invention aredescribed centering on the data transmission/reception relations betweena base station and a user equipment. In this case, the base stationmeans a terminal node of a network directly performing a communicationwith the user equipment. In this disclosure, a specific operationexplained as performed by a base station can be occasionally performedby an upper node of the base station.

In particular, in a network constructed with a plurality of networknodes including a base station, it is apparent that various operationsperformed for communication with a user equipment can be performed by abase station or other networks except the base station. In this case,‘base station’ can be replaced by such a terminology as a fixed station,a Node B, an eNode B (eNB), an access point, and the like. A relay canbe replaced by such a terminology as a relay node (RN), a relay station(RS), and the like. And, ‘terminal’ can be replaced by such aterminology as a user equipment (UE), a mobile station (MS), a mobilesubscriber station (MSS), a subscriber station (SS), and the like.

Specific terminologies used in the following description are provided tohelp the understanding of the present invention and can be modified to adifferent form in a scope of not deviating from the technical idea ofthe present invention.

Occasionally, to prevent the present invention from getting vaguer,structures and/or devices known to the public are skipped or can berepresented as block diagrams centering on the core functions of thestructures and/or devices. Wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or like parts.

Embodiments of the present invention can be supported by the standarddocuments disclosed in at least one of IEEE 802 system, a 3GPP system,3GPP LTE/LTE-A (LTE-Advanced), and a 3GPP2 system, which correspond towireless access systems. In particular, steps or parts among theembodiments of the present invention, which are not explained to clearlydisclose the technical idea of the present invention, can be supportedby the documents. And, all terminologies disclosed in the presentspecification can be explained by the standard document.

The following description of embodiments of the present invention mayapply to various wireless access systems including CDMA (code divisionmultiple access), FDMA (frequency division multiple access), TDMA (timedivision multiple access), OFDMA (orthogonal frequency division multipleaccess), SC-FDMA (single carrier frequency division multiple access) andthe like. CDMA can be implemented with such a radio technology as UTRA(universal terrestrial radio access), CDMA 2000 and the like. TDMA canbe implemented with such a radio technology as GSM/GPRS/EDGE (GlobalSystem for Mobile communications)/General Packet Radio Service/EnhancedData Rates for GSM Evolution). OFDMA can be implemented with such aradio technology as IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE802.20, E-UTRA (Evolved UTRA), etc. UTRA is a part of UMTS (UniversalMobile Telecommunications System). 3GPP (3rd Generation PartnershipProject) LTE (long term evolution) is a part of E-UMTS (Evolved UMTS)that uses E-UTRA and adopts OFDMA in downlink and adopts SC-FDMA inuplink. LTE-A (LTE-Advanced) is an evolved version of 3GPP LTE. WiMAXcan be explained by IEEE 802.16e standard (WirelessMAN-OFDMA ReferenceSystem) and advanced IEEE 802.16m standard (WirelessMAN-OFDMA AdvancedSystem). For clarity, the following description mainly concerns 3GPP LTEsystem or 3GPP LTE-A system, by which the technical idea of the presentinvention may be non-limited.

A structure of a downlink radio frame is explained with reference toFIG. 2, including view (a) and view (b).

In a cellular OFDM radio packet communication system, UL/DL(uplink/downlink) data packet transmission is performed by a unit ofsubframe. And, one subframe is defined as a predetermined time intervalincluding a plurality of OFDM symbols. In the 3GPP LTE standard, atype-1 radio frame structure applicable to FDD (frequency divisionduplex) and a type-2 radio frame structure applicable to TDD (timedivision duplex) are supported.

FIG. 2(a) is a diagram for a structure of a downlink radio frame oftype 1. A DL (downlink) radio frame includes 10 subframes. Each of thesubframes includes 2 slots. And, a time taken to transmit one subframeis defined as a transmission time interval (hereinafter abbreviatedTTI). For instance, one subframe may have a length of 1 ms and one slotmay have a length of 0.5 ms. One slot may include a plurality of OFDMsymbols in time domain and may include a plurality of resource blocks(RBs) in frequency domain. Since 3GPP LTE system uses OFDMA in downlink,OFDM symbol is provided to indicate one symbol period. The OFDM symbolmay be named SC-FDMA symbol or symbol period. Resource block (RB) is aresource allocation unit and may include a plurality of contiguoussubcarriers in one slot.

The number of OFDM symbols included in one slot may vary in accordancewith a configuration of a cyclic prefix (CP). The CP may be categorizedinto an extended CP and a normal CP. For instance, in case that OFDMsymbols are configured by the normal CP, the number of OFDM symbolsincluded in one slot may be 7. In case that OFDM symbols are configuredby the extended CP, since a length of one OFDM symbol increases, thenumber of OFDM symbols included in one slot may be smaller than that ofthe case of the normal CP. In case of the extended CP, for instance, thenumber of OFDM symbols included in one slot may be 6. If a channelstatus is unstable (e.g., a UE is moving at high speed), it may be ableto use the extended CP to further reduce the inter-symbol interference.

When a normal CP is used, since one slot includes 7 OFDM symbols, onesubframe includes 14 OFDM symbols. In this case, first 2 or 3 OFDMsymbols of each subframe may be allocated to PDCCH (physical downlinkcontrol channel), while the rest of the OFDM symbols are allocated toPDSCH (physical downlink shared channel).

FIG. 2(b) is a diagram for a structure of a downlink radio frame of type2. A type-2 radio frame includes 2 half frames. Each of the half frameconsists of 5 subframes, a downlink pilot time slot (DwPTS), a guardperiod (GP), and an uplink pilot time slot (UpPTS) and one subframeconsists of two slots. The DwPTS is used for initial cell search,synchronization or channel estimation in a user equipment. The UpPTS isused for channel estimation in a base station and uplink transmissionsynchronization of a user equipment. The guard period is a period foreliminating interference generated in uplink due to multi-path delay ofa downlink signal between uplink and downlink. Meanwhile, one subframeconsists of two slots irrespective of a type of a radio frame.

The above-described structures of the radio frame are exemplary only.And, the number of subframes included in a radio frame, the number ofslots included in the subframe and the number of symbols included in theslot may be modified in various ways.

FIG. 3 is a diagram for a resource grid in a downlink slot. One downlink(DL) slot includes 7 OFDM symbols in time domain and one resource block(RB) includes 12 subcarriers in frequency domain, by which the presentinvention may be non-limited. For instance, in case of a normal CP(cyclic prefix), one slot includes 7 OFDM symbols. In case of anextended CP, one slot may include 6 OFDM symbols. Each element on aresource grid is called a resource element. One resource block includes12×7 resource elements. The number N^(DL) of resource blocks included ina DL slot may depend on a DL transmission bandwidth. And, the structureof an uplink (UL) slot may be identical to that of the DL slot.

FIG. 4 is a diagram for a structure of a downlink subframe. Maximum 3OFDM symbols situated in a head part of a first slot of one subframecorrespond to a control region to which control channels are allocated.The rest of OFDM symbols correspond to a data region to which PDSCH(physical downlink shared channel) is allocated. Examples of DL controlchannels used by 3GPP LTE may include PCFICH (Physical Control FormatIndicator Channel), PDCCH (Physical Downlink Control Channel), PHICH(Physical hybrid automatic repeat request indicator Channel) and thelike. The PCFICH is transmitted in a first OFDM symbol of a subframe andincludes information on the number of OFDM symbols used for atransmission of a control channel within the subframe. The PHICH is aresponse channel in response to UL transmission and includes ACK/NACK(acknowledgement/non-acknowledgement) signal for HARQ (hybrid automaticrepeat request). Control information carried on PDCCH may be calleddownlink control information (hereinafter abbreviated DCI). The DCI mayinclude UL scheduling information, DL scheduling information, or a ULtransmit power control command for a random UE (user equipment) group.PDCCH is able to include a transmission format of DL-SCH (downlinkshared channel) and resource allocation, resource allocation informationon UL-SCH (uplink shared channel), paging information on PCH (pagingchannel), system information on DL-SCH, resource allocation informationof an upper layer control message such as a random access responsetransmitted on PDSCH, a set of a transmit power control command forindividual user equipments within a random user equipment (UE) group,transmit power control information, activation of VoIP (voice over IP)and the like. A plurality of PDCCHs can be transmitted in a controlregion and a user equipment is able to monitor a plurality of thePDCCHs. PDCCH is transmitted with the aggregation of at least one ormore contiguous CCEs (control channel elements). CCE is a logicalassignment unit used to provide PDCCH with a code rate in accordancewith a state of a radio channel. CCE corresponds to a plurality of REGs(resource element groups). A format of PDCCH and the number of bits ofan available PDCCH are determined depending on correlation between thenumber of CCEs and a code rate provided by the CCEs. A base stationdetermines PDCCH format in accordance with DCI transmitted to a userequipment and attaches CRC (cyclic redundancy check) to controlinformation. The CRC is masked with a unique identifier (called RNTI(radio network temporary identifier)) in accordance with an owner orusage of PDCCH. If the PDCCH is provided for a specific user equipment,the CRC can be masked with a unique identifier of the user equipment,i.e., C-RNTI (i.e., Cell-RNTI). As a different example, if the PDCCH isprovided for a paging message, the CRC can be masked with a pagingindication identifier (e.g., P-RNTI (Paging-RNTI)). If the PDCCH isprovided for system information (more specifically, for a systeminformation block (SIB)), the CRC can be masked with a systeminformation identifier (e.g., SI-RNTI (system information-RNTI)). Inorder to indicate a random access response that is a response to atransmission of a random access preamble of a user equipment, CRC can bemasked with RA-RNTI (random access-RNTI).

FIG. 5 is a diagram for a structure of an uplink subframe. A UL subframemay be divided into a control region and a data region in frequencydomain. PUCCH (physical uplink control channel) including UL controlinformation is assigned to the control region. PUSCH (physical uplinkshared channel) including a user data is assigned to the data region. Inorder to maintain single carrier characteristic, a user equipment doesnot transmit PUCCH and PUSCH at the same time. PUCCH for one userequipment is assigned to a resource block pair (RB pair) in a subframe.Resource blocks belonging to the RB pair occupy a subframe differentfrom each other for 2 slots. This is called that the RB pair assigned toPUCCH is frequency-hopped on a slot boundary.

Modeling of Multi-Antenna (MIMO) System

FIG. 6, including view (a) and view (b), is a structured diagram of aradio communication system having multiple antennas.

As depicted in FIG. 6(a), unlike a case that a plurality of antennas areused in either a transmitter or a receiver only, if the number oftransmitting antenna and the number of receiving antenna are increasedto N_(T) and N_(R), respectively, a theoretical channel transmissioncapacity is increased in proportional to the number of antenna.Consequently, a transfer rate is enhanced and frequency efficiency isdramatically enhanced. As the channel transmission capacity increases,the transfer rate can be theoretically increased as much as the maximumtransfer rate (R_(o)) in case of using a single antenna multiplied by arate of increase (R_(i)).R _(i)=min(N _(T) ,N _(R))  [Formula 1]

For instance, MIMO communication system using 4 transmitting antennasand 4 receiving antennas may be able to theoretically obtain thetransfer rate of 4 times of a single antenna system. After thetheoretical capacity increase of the multi-antenna system is proved inthe mid-90s, various technologies for practically enhancing a datatransmission rate have been actively studied up to date and severaltechnologies among them are already reflected in such a various wirelesscommunication standard as a 3^(rd) generation mobile communication, anext generation wireless LAN and the like.

If we look at the research trend related to the multi-antenna until now,many active researches have been performed for such a study of variouspoints of view as a study on information theory related to amulti-antenna communication capacity calculation in various channelenvironments and multiple access environment, a study on a radio channelmeasurement and model deduction of the multi-antenna system, a study ona space-time signal processing technology for enhancing a transmissionreliability and a transmission rate, and the like.

A communication method in the multi-antenna system is explained in moredetail using a mathematical modeling. Assume that there exist N_(T)number of transmitting antenna and N_(R) number of receiving antenna inthe system.

First of all, if we look into a transmission signal, in case that thereexists N_(T) number of transmitting antenna, transmission informationcan be represented as a vector in the following Formula 2.s=└s ₁ ,s ₂ , . . . ,s _(N) _(T) ┘^(T)  [Formula 2]

Meanwhile, for each of the transmission information s₁, s₂, . . . ,s_(N) _(T) , a transmit power may vary according to the each of thetransmission information. In this case, if each of the transmit powersis represented as P₁, P₂, . . . , P_(N) _(T) , transmit power-adjustedtransmission information can be represented as a vector in the followingFormula 3.ŝ=[ŝ ₁ ,ŝ ₂ , . . . ,ŝ _(N) _(T) ]^(T) =[P ₁ s ₁ ,P ₂ s ₂ , . . . ,P_(N) _(T) s _(N) _(T) ]^(T)  [Formula 3]

And, if ŝ is represented using a diagonal matrix P, it can berepresented as a following Formula 4.

$\begin{matrix}{\hat{s} = {{\begin{bmatrix}P_{1} & \; & \; & 0 \\\; & P_{2} & \; & \; \\\; & \; & \ddots & \; \\0 & \; & \; & P_{N_{T}}\end{bmatrix}\begin{bmatrix}s_{1} \\s_{2} \\\vdots \\s_{N_{T}}\end{bmatrix}} = {Ps}}} & \left\lbrack {{Formula}\mspace{14mu} 4} \right\rbrack\end{matrix}$

Meanwhile, let's consider a case that the N_(T) number of transmissionsignal x₁, x₂, . . . , x_(N) _(T) , which is practically transmitted, isconfigured in a manner of applying a weighted matrix W to the adjustedinformation vector ŝ. In this case, the weighted matrix W plays a rolein distributing the transmission information to each of the antennasaccording to the situation of the transmission channel and the like. Thetransmission signal x₁, x₂, . . . , x_(N) _(T) can be represented usinga vector X in the following Formula 5.

$\begin{matrix}{x = {\begin{bmatrix}x_{1} \\x_{2} \\\vdots \\x_{i} \\\vdots \\x_{N_{T}}\end{bmatrix} = {{{\quad{{\begin{bmatrix}w_{11} & w_{12} & \ldots & w_{1N_{T}} \\w_{21} & w_{22} & \ldots & w_{2N_{T}} \\\vdots & \; & \ddots & \; \\w_{i\; 1} & w_{i\; 2} & \ldots & W_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\w_{N_{T}1} & w_{N_{T}2} & \ldots & w_{N_{T}N_{T}}\end{bmatrix}\begin{bmatrix}{\hat{s}}_{1} \\{\hat{s}}_{2} \\\vdots \\{\hat{s}}_{j} \\\vdots \\{\hat{s}}_{N_{T}}\end{bmatrix}} =}\quad}W\hat{s}} = {WPs}}}} & \left\lbrack {{Formula}\mspace{14mu} 5} \right\rbrack\end{matrix}$

In this case, W_(ij) means a weighting between an i^(th) transmittingantenna and j^(th) information. The W is called a precoding matrix aswell.

If there exists N_(R) number of receiving antenna, a reception signalfor each antenna can be represented as a vector in the following Formula6.y=[y ₁ ,y ₂ , . . . ,y _(N) _(R) ]^(T)  [Formula 6]

In case of modeling a channel in a multi-antenna wireless communicationsystem, the channel can be distinguished by a transmitting and receivingantenna index. The channel passing through a transmitting antenna j toreceiving antenna i is represented as h_(ij). According to the h_(ij),it should be cautious that a receiving antenna index comes first and atransmitting antenna index comes later.

Meanwhile, FIG. 6(b) is a diagram of channels passing through from N_(T)number of transmitting antennas to the receiving antenna i. The channelscan be represented as a vector and a matrix form in a manner of beingcollected. According to FIG. 6(b), a channel starting from the totalN_(T) number of transmitting antennas and arriving at the receivingantenna i can be represented as follows.h _(i) ^(T) =[h _(i1) ,h _(i2) , . . . ,h _(iN) _(T) ]  [Formula 7]

Hence, all channels starting from the N_(T) number of transmittingantennas and arriving at the N_(R) number of receiving antennas can berepresented as follows.

$\begin{matrix}{H = {\begin{bmatrix}h_{1}^{T} \\h_{2}^{T} \\\vdots \\h_{i}^{T} \\\vdots \\h_{N_{R}}^{T}\end{bmatrix} = \begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1N_{T}} \\h_{21} & h_{22} & \ldots & h_{2N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 1} & h_{i\; 2} & \ldots & h_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}}} & \left\lbrack {{Formula}\mspace{14mu} 8} \right\rbrack\end{matrix}$

Practically, after passing through the channel matrix H, an AdditiveWhite Gaussian Noise (AWGN) is added to the channel. The Additive WhiteGaussian Noise (AWGN) added to the each of the N_(R) number of receivingantennas can be represented as follows.n=[n ₁ ,n ₂ , . . . ,n _(N) _(R) ]^(T)  [Formula 9]

According to the aforementioned mathematical modeling, a receptionsignal can be represented as follows.

$\begin{matrix}{y = {\begin{bmatrix}y_{1} \\y_{2} \\\vdots \\y_{i} \\\vdots \\y_{N_{R}}\end{bmatrix} = {{{\begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1N_{T}} \\h_{21} & h_{22} & \ldots & h_{2N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 1} & h_{i\; 2} & \ldots & h_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}\left\lbrack \begin{matrix}x_{1} \\x_{2} \\\vdots \\x_{j} \\\vdots \\x_{N_{T}}\end{matrix} \right\rbrack} + \begin{bmatrix}n_{1} \\n_{2} \\\vdots \\n_{i} \\\vdots \\n_{N_{R}}\end{bmatrix}} = {{Hx} + n}}}} & \left\lbrack {{Formula}\mspace{14mu} 10} \right\rbrack\end{matrix}$

Numbers of column and row of the channel matrix H, which indicates astate of a channel, is determined by the number oftransmitting/receiving antenna. In the channel matrix H, the number ofrow corresponds to the number of receiving antennas N_(R) and the numberof column corresponds to the number of transmitting antennas N_(T). Inparticular, the channel matrix H corresponds to a matrix of N_(R)×N_(T).

Since a rank of the channel matrix is defined by a minimum number of thenumbers of row or column independent from each other, the rank of thematrix is configured not to be greater than the number of the row or thecolumn. The rank rank(H) of the channel matrix H is restricted asfollows.rank(H)≤min(N _(T) ,N _(R))  [Formula 11]

According to a different definition for a rank, the rank can be definedby the number of Eigen values, which is not 0, when a matrix isprocessed by Eigen value decomposition. Similarly, according to afurther different definition for a rank, the rank can be defined by thenumber of singular values, which is not 0, when a matrix is processed bysingular value decomposition. Hence, physical meaning of the rank in thechannel matrix may correspond to a maximum number capable oftransmitting information different from each other in a given channel.

Coordinated Multi-Point (CoMP)

According to an improved system performance requirement of a 3GPP LTE-Asystem, a CoMP transmission/reception technology MIMO (represented as aco-MIMO, a collaborative MIMO, a network MIMO, or the like) is proposed.The CoMP technology increases the performance of a user equipmentsituating at a cell edge and can increase an average sector throughput.

In general, in a multi-cell environment where a frequency reuse factorcorresponds to 1, the performance of a user equipment situating at acell boundary and the average sector throughput can be reduced due tointer-cell interference (ICI). In order to reduce the ICI, a legacy LTEsystem applied a method for enabling the user equipment situating at acell boundary to have an appropriate throughput performance using such asimple passive scheme as a fractional frequency reuse (FFR) via aUE-specific power control in an environment limited by the interference.Yet, it may be more preferable to reduce the ICI or reuse the ICI as asignal that the user equipment wants than to lower the use of afrequency resource per cell. In order to achieve the aforementionedpurpose, CoMP transmission scheme can be applied.

The CoMP scheme applicable in DL can be largely classified into a jointprocessing (JP) scheme and a coordinated scheduling/beamforming (CS/CB)scheme.

The JP scheme can use a data in each point (base station) of a CoMPcooperative unit. The CoMP cooperative unit means a set of base stationsused for a cooperative transmission scheme. The JP scheme can beclassified into a joint transmission scheme and a dynamic cell selectionscheme.

The joint transmission scheme indicates a scheme transmitting PDSCH froma plurality of points (a part or entire CoMP cooperative units) at atime. In particular, the data transmitted to single user equipment canbe simultaneously transmitted from a plurality of transmission points.According to the joint transmission scheme, quality of a receptionsignal can be coherently or non-coherently enhanced. And, interferencefor a different user equipment can be actively eliminated.

The dynamic cell selection scheme indicates a scheme transmitting PDSCHfrom a point (of a CoMP cooperative unit) at a time. In particular, adata transmitted to single user equipment on a specific timing point istransmitted from one point. A different point within the cooperativeunit does not transmit a data to the corresponding user equipment on thespecific timing point. The point transmitting the data to thecorresponding user equipment can be dynamically selected.

Meanwhile, according to CS/CB scheme, the CoMP cooperative units cancooperatively perform a beamforming of data transmission for single userequipment. In this case, although the data is transmitted from a servingcell only, a user scheduling/beamforming can be determined by acoordination of cells in a corresponding CoMP cooperative unit.

Meanwhile, in case of UL, a coordinated multi-point reception means toreceive a signal transmitted by coordination of a plurality of points,which are geographically apart from each other. The CoMP schemeapplicable to a case of UL can be classified into a joint reception (JR)and the coordinated scheduling/beamforming (CS/CB).

The JR scheme means that a signal transmitted on PUSCH is received by aplurality of receiving points. The CS/CB scheme means that PUSCH isreceived at one point and a user scheduling/beamforming is determined bycoordination of cells in a CoMP cooperative unit.

If the aforementioned CoMP system is used, a user equipment can bejointly supported with a data from a multi-cell base station. And, bysimultaneously supporting at least one user equipment using a same radiofrequency resource, each base station can enhance system performance.And, the base station may perform a space division multiple access(SDMA) scheme based on channel state information between the basestation and the user equipment.

In a CoMP system, a serving base station and one or more cooperativebase stations are connected to a scheduler via a backbone network. Thescheduler can operate in a manner of being fed back channel informationon a channel state between a user equipment and a cooperative basestation, which is measured by the each base station via the backbonenetwork. For instance, the scheduler can schedule information for theserving base station and one or more cooperative base stations toperform a cooperative MIMO operation. In particular, the scheduler candirectly give a direction for the cooperative MIMO operation to eachbase station.

As mentioned in the foregoing description, the CoMP system maycorrespond to a virtual MIMO system operating in a manner of bundling upa plurality of cells into a group. Basically, a communication techniqueof a MIMO system using multi-antenna can be applied to the CoMP system.

Downlink Channel State Information (CSI) Feedback

A MIMO scheme can be divided into an open-loop scheme and a closed-loopscheme. The open-loop MIMO scheme means to perform MIMO transmission ina transmitting end without a feedback of channel state information froma MIMO receiving end. The closed-loop MIMO scheme means to perform theMIMO transmission in the transmitting end by receiving the feedback ofthe channel state information from the MIMO receiving end. Each of thetransmitting end and the receiving end can perform beamforming based onthe channel state information to obtain multiplexing gain of the MIMOtransmission antenna in the closed-loop MIMO scheme. The transmittingend (e.g., base station) can assign a UL control channel or a UL sharedchannel to the receiving end (e.g., UE) in order for the receiving end(e.g., UE) to feedback the channel state information.

The channel state information (CSI) to be fed back may include a rankindicator (RI), a precoding matrix index (PMI), and a channel qualityindicator (CQI).

The RI corresponds to information on a channel rank. The channel rankmeans maximum numbers of layer (or stream) capable of transmittinginformation different from each other via an identical time-frequencyresource. Since a rank value is mainly determined by a long term fadingof a channel, the rank value can be fed back with a longer interval(i.e., less frequently) compared to the PMI and the CQI in general.

The PMI corresponds to information on a precoding matrix used fortransmitting from the transmitting end. The PMI is a value reflectingcharacteristics of space of a channel. A precoding means to map atransmission layer to a transmission antenna and a layer-antenna mappingrelationship can be determined by a precoding matrix. The PMIcorresponds to a precoding matrix index of a base station preferred by auser equipment on the basis of such a measurement value (metric) assignal-to-interference plus noise ratio (SINR) and the like. In order toreduce feedback overhead of precoding information, a method of sharing acodebook shared by the transmitting end and the receiving end includingvarious precoding matrices in advance and performing a feedback of anindex for indicating a specific precoding matrix of the correspondingcodebook only.

The CQI corresponds to information indicating channel quality or channelstrength. The CQI can be represented by a combination of a predeterminedmodulation and coding scheme (MCS). In particular, a CQI index to be fedback may indicate a corresponding modulation scheme and a code rate. Ingeneral, the CQI may become a value reflecting a reception SINR, whichis obtainable in case that a base station forms a spatial channel usingthe PMI.

A system supporting an expanded antenna configuration (e.g., LTE-Asystem) considers obtaining additional multi-user diversity by using amultiple user-MIMO (MU-MIMO) scheme. Since interference channel existsbetween user equipments, which are multiplexed in an antenna domain, inthe MU-MIMO scheme, if a base station performs a DL transmission usingthe channel state information fed back by one user equipment of themultiple users, it is necessary to make interference for a differentuser equipment not occur. Hence, in order to properly perform an MU-MIMOoperation, channel state information having higher accuracy compared toa single user-MIMO (SU-MIMO) scheme should be fed back.

As mentioned in the foregoing description, in order to measure andreport more accurate channel state information, a new CSI feedbackmethod, which is upgraded from the CSI consisted of a conventional RI,the PMI, and the CQI, can be applied. For instance, the precodinginformation fed back by the receiving end can be indicated by acombination of 2 PMIs. One (first PMI) of the 2 PMIs including aproperty of long term and/or wideband can be called a W1. Another one(second PMI) of the 2 PMIs including a property of short term and/orsubband can be called a W2. A final PMI can be determined by acombination (or function) of the W1 and the W2. For instance, if thefinal PMI corresponds to W, it can be defined as ‘W=W1*W2’ or ‘W=W2*W1’.

In this case, the W1 reflects a frequency of a channel and/or an averagecharacteristic on time. In other word, the W1 can be defined as thechannel state information reflecting a characteristic of a long termchannel on time, a characteristic of a wideband channel on frequency, orboth the characteristic of a long term channel on time and thecharacteristic of a wideband channel on frequency. In order to brieflyrepresent the characteristic of the W1, the present specification callsthe W1 as the channel state information of long term-wideband property(or, long term-wideband PMI).

Meanwhile, the W2 reflects relatively instantaneous channelcharacteristic compared to the W1. In other word, the W2 can be definedas the channel state information reflecting a characteristic of a shortterm channel on time, a characteristic of a subband channel onfrequency, or both the characteristic of a short term channel on timeand the characteristic of a subband channel on frequency. In order tobriefly represent the characteristic of the W2, the presentspecification calls the W2 as the channel state information of shortterm-subband property (or, short term-subband PMI).

In order to determine one final precoding matrix (W) from theinformation (e.g., the W1 and the W2) of 2 properties different fromeach other indicating channel state, it is necessary to configure aseparate codebook (in particular, a first codebook for the W1 and asecond codebook for the W2) consisted of precoding matrices indicatingthe channel information of each property. A form of the codebookconfigured according to the aforementioned way can be called ahierarchical codebook. And, to determine a codebook to be finally usedusing the hierarchical codebook can be called a hierarchical codebooktransformation.

As an example of the hierarchical transformation, a codebook can betransformed using a long term covariance matrix of a channel as shown inthe following Formula 12.W=norm(W1W2)  [Formula 12]

In Formula 12, the W1 (long term-wideband PMI) indicates an element(i.e., codeword) constructing a codebook (e.g., first codebook) designedto reflect the channel information of a long term-wideband property. Inparticular, the W1 corresponds to a precoding matrix included in thefirst codebook reflecting the channel information of the longterm-wideband. Meanwhile, the W2 (short term-subband PMI) indicates acodeword constructing a codebook (e.g., second codebook) designed toreflect the channel information of a short term-subband property. Inparticular, the W2 corresponds to a precoding matrix included in thesecond codebook reflecting the channel information of the shortterm-subband. W indicates a codeword of a final transformed codebook.norm (A) means a matrix that a norm according to each column of a matrixA is normalized to 1.

For instance, the W1 and the W2 may have a structure shown in thefollowing Formula 13.

$\begin{matrix}{{{{W\; 1(i)} = \begin{bmatrix}X_{i} & 0 \\0 & X_{i}\end{bmatrix}}{W\; 2(j)} = \overset{\underset{︷}{r\mspace{14mu}{columns}}}{\begin{bmatrix}e_{M}^{k} & e_{M}^{l} & \ldots & e_{M}^{m} \\{\alpha_{j}e_{M}^{k}} & {\beta_{j}e_{M}^{l}} & \; & {\gamma_{j}e_{M}^{m}}\end{bmatrix}}}\left( {{{if}\mspace{14mu}{rank}} = r} \right)} & \left\lbrack {{Formula}\mspace{14mu} 13} \right\rbrack\end{matrix}$

In Formula 13, the W1 can be defined as a form of a block diagonalmatrix and each block corresponds to an identical matrix (X_(i)). Oneblock (X_(i)) can be defined as a matrix of (N_(t)/2)×M size. In thiscase, the N_(t) corresponds to the number of transmitting antenna. InFormula 13, e_(M) ^(p) (p=k, l, . . . , m) of the W2 is a vector of M×1size. The vector indicates that p^(th) component is 1 and the rest ofcomponents are 0 among the M number of vector components. In case ofmultiplying the e_(M) ^(p) by the W1, since the p^(th) column isselected among the columns of the W1, this sort of vector is called aselection vector. In this case, as a value of M increases, the number ofvectors fed back at a time increases to represent the long term/widebandchannel. By doing this, feedback accuracy becomes higher. Yet, as thevalue of M increases, the codebook size of the W1, which is fed backwith low frequency, is diminished and the codebook size of the W2, whichis fed back with high frequency, is increased. As a result, feedbackoverhead increases. In particular, there exists a tradeoff between thefeedback overhead and the feedback accuracy. Hence, the M value can bedetermined not to make the feedback overhead increase too much whilemaintaining appropriate feedback accuracy. Meanwhile, α_(j), β_(j),γ_(j) of the W2 indicate prescribed phase values, respectively. InFormula 13, ‘1≤k, l, m≤M’ and each of k, l, m is an integer.

The codebook structure shown in Formula 13 is a structure designed towell reflect a correlation property of a channel, which occurs in casethat a cross polarized (X-pol) antenna configuration is used and a spacebetween antennas is dense (commonly, in case that a distance betweenneighboring antennas is less than a half of a signal wavelength). Forinstance, the cross-polarized antenna configuration can be representedas a Table 1 as follows.

TABLE 1 2Tx cross-polarized antenna configuration

4Tx cross-polarized antenna configuration

8Tx cross-polarized antenna configuration

In Table 1, an 8Tx cross-polarized antenna configuration can berepresented as the 8Tx cross-polarized antenna configuration isconfigured with 2 antenna groups having a property of orthogonal to eachother. Antennas (antenna 1, 2, 3, and 4) of an antenna group 1 have anidentical polarization (e.g., vertical polarization) and antennas(antenna 5, 6, 7, and 8) of an antenna group 2 may have an identicalpolarization (e.g., horizontal polarization). And, the two antennagroups are located at an identical location (co-located). For instance,antenna 1 and 5 can be installed in a same place, antenna 2 and 6 can beinstalled in a same place, antenna 3 and 7 can be installed in a sameplace, and antenna 4 and 8 can be installed in a same place. In otherword, the antennas belonging to one antenna group have an identicalpolarization such as a uniform linear array (ULA) and correlationbetween antennas within one antenna group has a property of linear phaseincrement. And, correlation between antenna groups has a property ofphase rotation.

Since a codebook corresponds to a quantized channel value, it isnecessary to design the codebook in a manner of reflecting thecharacteristic of a practical channel as it is. In order to explain thatthe characteristic of practical channel is reflected to the codeword ofthe codebook designed like Formula 13, a rank 1 codebook is explained asan example. In the following description, Formula 14 indicates anexample that a final codeword (W) is determined in a manner ofmultiplying a W1 codeword by a W2 codeword in case of a rank 1.

$\begin{matrix}{{W\; 1(i)*W\; 2(j)} = \begin{bmatrix}{X_{i}(k)} \\{\alpha_{j}{X_{i}(k)}}\end{bmatrix}} & \left\lbrack {{Formula}\mspace{14mu} 14} \right\rbrack\end{matrix}$

In Formula 14, the final codeword is represented by a vector of N_(t)×1and is structured by two vectors corresponding to a upper vectorX_(i)(k) and a lower vector α_(j)X_(i)(k). The upper vector X_(i)(k)indicates the correlation characteristic of a horizontal polarizationantenna group of a cross polarization antenna and the lower vectorα_(j)X_(i)(k) indicates the correlation characteristic of a verticalpolarization antenna group. And, the X_(i)(k) can be represented by avector (e.g., DFT matrix) having linear phase increment by reflectingthe correlation characteristic between antennas belonging to each of thegroups.

In case of using the aforementioned codebook, it enables to perform achannel feedback of higher accuracy compared to a case of using a singlecodebook. Hence, a single-cell MU-MIMO may be enabled by using thechannel feedback of higher accuracy. With a similar reason, CoMPoperation requires a channel feedback of higher level of accuracy aswell. For instance, In case of a CoMP JT operation, since a plurality ofbase stations cooperatively transmit an identical data to a specific UE,it can be theoretically considered as a MIMO system where a plurality ofantennas are geographically distributed. In particular, similar to thesingle-cell MU-MIMO, in case of performing a MU-MIMO operation in theCoMP JT, high level of accuracy of channel information is required toavoid interference between co-scheduled UEs. And, in case of a CoMP CBoperation, elaborate channel information is required as well to avoidthe interference affecting a serving cell by a neighboring cell.

Inter-Cell Interference Coordination (ICIC)

Interference between neighboring cells may cause a problem in theaforementioned heterogeneous network environment and/or the CoMPenvironment. In order to solve the problem of inter-cell interference,inter-cell interference coordination can be applied. A conventional ICICcan be applied to a frequency resource or a time resource.

As an example of the ICIC for the frequency resource, 3GPP LTE release-8system divides a given whole frequency domain (e.g., system bandwidth)into one or more sub domains (e.g., physical resource block (PRB) unit)and defines a method of exchanging an ICIC message for each of thefrequency sub domains between cells. For instance, as the informationincluded in the ICIC message for the frequency resource, relativenarrowband transmission power (RNTP) related to a DL transmit power isdefined and UL interference overhead indication (IOI) related to ULinterference, UL high interference indication (HII), and the like aredefined in the 3GPP LTE release-8 system.

The RNTP is the information indicating DL transmit power used by a celltransmitting an ICIC message on a specific frequency sub domain. Forinstance, if an RNTP field for the specific frequency sub domain is setto a first value (e.g., 0), it may mean that the DL transmit power of acorresponding cell does not exceed a prescribed threshold on thecorresponding frequency sub domain. Or, if the RNTP field for thespecific frequency sub domain is set to a second value (e.g., 1), it maymean that the corresponding cell cannot promise the DL transmit power onthe corresponding frequency sub domain. In other word, if the value ofthe RNTP field corresponds to 0, the DL transmit power of thecorresponding cell can be considered to be low. Yet, if the value of theRNTP field corresponds to 1, the DL transmit power of the correspondingcell cannot be considered to be low.

The UL IOI is the information indicating an amount of UL interferenceexperienced (or received) by a cell transmitting an ICIC message on thespecific frequency sub domain. For instance, if an IOI field for thespecific frequency sub domain is set to a value corresponding to a largeamount of interference, it may mean that the corresponding cell isexperiencing strong UL interference on the frequency sub domain. Havingreceived the ICIC message, the cell can schedule a user equipment usinglow transmit power among the user equipments served by the cell on thefrequency sub domain corresponding to the IOI indicating strong ULinterference. By doing so, since the user equipments perform ULtransmission with a low transmit power on the frequency sub domaincorresponding to the IOI indicating the strong UL interference, the ULinterference experienced by a neighboring cell (i.e., the celltransmitted the ICIC message) can be reduced.

The UL HII is the information indicating an extent of interference (or,UL interference sensitivity) capable of being occurred by a ULtransmission for a corresponding frequency sub domain in a celltransmitting the ICIC message. For instance, if a HII field is set to afirst value (e.g., 1) for a specific frequency sub domain, it may meanthat the cell transmitting the ICIC message is likely to schedule a userequipment of a strong UL transmit power for the corresponding frequencysub domain. On the other hand, if the HII field is set to a second value(e.g., 0) for the specific frequency sub domain, it may mean that thecell transmitting the ICIC message is likely to schedule a userequipment of a weak UL transmit power for the corresponding frequencysub domain. Meanwhile, having received the ICIC message, the cellpreferentially schedules a user equipment for the frequency sub domainwhere the HII field is set to the second value (e.g., 0) and schedules auser equipment capable of well operating despite of strong interferencefor the frequency sub domain where the FII field is set to the firstvalue (e.g., 1), thereby avoiding the interference from the celltransmitted the ICIC message.

Meanwhile, as an example of an ICIC for the time resource, 3GPP LTErelease-10 system divides a given whole time domain into one or more subdomains (e.g., subframe unit) and defines a method of exchanging whethereach of the time sub domains is silent between cells. The celltransmitting an ICIC message can deliver the information indicating thata silencing is performed in a specific subframe to neighbor cells anddoes not schedule PDSCH or PUSCH in the corresponding subframe.Meanwhile, a cell receiving the ICIC message can schedule UL and/or DLtransmission for a user equipment in the subframe where the silencing isperformed in the cell transmitted the ICIC message.

The silencing may mean that a specific cell does not perform (orperforms transmission of 0 or weak power) an operation of most of signaltransmission in UL and DL in a specific subframe. As an example of thesilencing operation, the specific cell can configure the specificsubframe as a multicast broadcast single frequency network (MBSFN)subframe. In a DL subframe configured as the MBSFN subframe, a signal istransmitted in a control region only and the signal is not transmittedin a data region. As a different example of the silencing operation, aninterfering cell may configure the specific subframe as an almost blanksubframe (ABS) or an ABS-with-MBSFN. The ABS means a subframetransmitting a CRS only in the control region and the data region of aDL subframe and the subframe where other control information and dataare not transmitted (or, performs transmission of a weak power only).Yet, such a DL channel as PBCH, PSS, SSS, and the like and a DL signalcan be transmitted in the ABS. The ABS-with-MBSFN indicates a case thatthe CRS of the data region is not transmitted in the aforementioned ABS.As mentioned in the foregoing description, the silencing can beperformed in a specific subframe unit and the information indicatingwhether the silencing is performed can be called a silent subframepattern.

And, a silent subframe explained in the embodiment of the presentinvention can be understood as a subframe to which no signal istransmitted or the subframe to which a weak signal is transmitted. Forclarity of explanation, although the silent subframe is exemplarilyexplained as the subframe to which no signal is transmitted in thefollowing description, the principle of the present invention can beidentically applied to a case that a signal of weak power is transmittedin the silent subframe as well.

As mentioned in the foregoing description, the ICIC information (e.g.,RNTP, IOI, HII) on the frequency resource is defined as the informationto be applied to a specific frequency sub domain in all subframeswithout an indication indicating which subframe is applied by theinformation. The ICIC information (e.g., silent subframe pattern) on thetime resource is defined as the information to be applied to allfrequency domain without an indication indicating which frequency domainis applied by the information. Hence, if one cell transmits both theICIC message for the frequency resource and the ICIC message for thetime resource to neighboring cells, the time and frequency resource towhich an ICIC operation is applied cannot be clearly specified. Forinstance, if it is considered both the information that a silencing isapplied in a specific subframe without decision for a frequency domainand the information that DL transmit power exceeds a prescribedthreshold value on a specific frequency sub domain without decision forthe time domain, it becomes impossible to determine whether a silencingis performed or a strong DL transmission is performed on a correspondingfrequency sub domain in a corresponding subframe.

In the following description, embodiments of the present inventionscapable of clearly determining which ICIC operation is performed in casethat the ICIC information on the frequency resource and the ICICinformation on the time resource exist in a manner of being mixed areexplained.

The present invention can specify a position of a different cell on atime resource based on a position where an ICIC operation of one cell isperformed in a manner of considering a difference of subframe timingeven in a case that a subframe boundary between cells is not matchedwith each other. The principle proposed by the present invention can beidentically applied based on the above mentioned. Yet, for clarity ofexplanation, assume that the subframe boundary of two cells performingthe ICIC operation is arrayed in the following description. Inparticular, assume that a start timing of a subframe of one cell ismatched with the start timing of a subframe of a different cell.

And, in the following description, a cell determining and transmitting asilent subframe pattern corresponds to an interfering cell (or aggressorcell) and a cell receiving a silent subframe pattern of a neighboringcell may correspond to an interfered cell (or victim cell).

Embodiment 1

The present embodiment describes an ICIC operation of each cell in casethat a silent subframe pattern of one cell is applied together with RNTPinformation.

For clarity of explanation, a cell transmitting ICIC information (e.g.,an RNTP, an IOI, an HII, or a silent subframe pattern) is called a firstcell and a cell receiving the ICIC information is called a second cellin the following description. In particular, assume that the first cellinforms the second cell of the information of the RNTP, the IOI, theHII, and the like of the first cell while informing the second cell ofthe subframe pattern of which a silencing is performed, by which thepresent embodiment may be non-limited to this. In case that the ICICinformation of one cell is received by one or more neighboring cells,the principle of the present invention can be identically applied.

FIG. 7 is a flowchart showing an example of the present invention for anICIC operation in case that ICIC information on a time and frequencyresource of one cell is delivered to a different cell.

In the step S710, the first cell determines frequency resource ICICinformation (e.g., RNTP) and time resource ICIC information (e.g.,silent subframe pattern) and can transmit the determined frequencyresource and time resource ICIC information to the second cell in thestep S720.

In the step S730, the second cell can assume validity of the frequencyresource ICIC information based on the time resource ICIC informationreceived from the first cell. For instance, if the first cell indicatesa DL subframe n as a silent subframe, it means that there is no PDSCHtransmission of the first cell in the subframe n. More specifically, itmeans that there is no PDSCH transmission of the first cell on allfrequency domains of the subframe n. Hence, since DL transmit power ofthe first cell in the subframe n is set to very low (in particular, onlythe power according to a minimum signal transmission) on all frequencydomains, it is preferable to assume that the RNTP information indicatingrelative strength of the transmit power of the first cell on the basisof a prescribed threshold value does not have any meaning in the RNTP.

Subsequently, the second cell can assume that there is no application ofthe RNTP indication of the first cell (or does not interpret the RNTPindication) in the DL subframe indicated by the first cell as the silentsubframe. Or, the second cell ignores the RNTP field value transmittedby the first cell for the silent subframe of the first cell and canoverride all frequency sub domains in a manner of setting the RNTP valueof the first cell to 0 (in particular, the DL transmit power is lowerthan a prescribed threshold value). In other word, it is possible to saythat the second cell considers the RNTP indication of the first cell asvalid only in the subframe(s) where the first cell did not configure thesubframe(s) as the silent subframe.

According to the method of considering the silent subframe patterntogether with the RNTP information in the foregoing description, in caseof the frequency sub domain (or, the frequency sub domain not indicatedthat the transmit power of the first cell is lower than a prescribedthreshold value) not received the content, which indicates thatinter-cell interference of the first cell will be reduced, via the RNTPindication, the second cell can freely perform a DL scheduling in thesubframe configured as the silent subframe by the first cell regardlessof the inter-cell interference [S730]. By doing this, efficiency ofresource utilization can be enhanced.

Although the first cell indicates an extent of DL transmit power of thefirst cell for a specific frequency sub domain, the first cell canpredict that the RNTP transmitted to the second cell is not valid in theDL subframe of which the first cell has configured it as the silentsubframe [S750]. In particular, the first cell anticipates that thesecond cell, which has received the RNTP, may cause strong interferencein DL for all frequency resources in the silent subframe of the firstcell irrespective of the RNTP and can perform DL scheduling of the firstcell.

Embodiment 2

The present embodiment describes an ICIC operation of each cell in casethat a silent subframe of one cell is applied together with IOI/HIIinformation. Since the present embodiment relates to UL transmission,the UL transmission and timing relationship between schedulinginformation transmission and the UL transmission are explained inadvance.

PUSCH transmission in UL subframe n+k can be performed according toscheduling information (i.e., UL grant information) received in DLsubframe n. In this case, in case of a FDD system, k value may be fixedto 4 and can be determined according to the following Table 2 and Table3 in case of a TDD system.

TABLE 2 Downlink- to-Uplink Uplink- Switch- downlink point Subframenumber configuration periodicity 0 1 2 3 4 5 6 7 9 9 0 5 ms D S U U U DS U U U 1 5 ms D S U U D D S U U D 2 5 ms D S U D D D S U D D 3 10 ms  DS U U U D D D D D 4 10 ms  D S U U D D D D D D 5 10 ms  D S U D D D D DD D 6 5 ms D S U U U D S U U D

TABLE 3 TDD UL/DL DL subtrame number n Configuration 0 1 2 3 4 5 6 7 8 90 4 6 4 6 1 6 4 6 4 2 4 4 3 4 4 4 4 4 4 5 4 6 7 7 7 7 5

Table 2 indicates the configuration for a UL subframe and a DL subframein a 3GPP LTE TDD system. In Table 2, D indicates a DL subframe, Uindicates a UL subframe, and S indicates a special subframe. The specialsubframe is a subframe including the DwPTS, the GP, and the UpPTSdescribed in FIG. 2. Meanwhile, Table 3 indicates transmission timingdifference (i.e., k) between PDCCH and PUSCH in a 3GPP LTE TDD system.For instance, in case of TDD UL/DL configuration 0, UL grant informationreceived on PDCCH in a DL subframe 5 may correspond to the schedulinginformation on PUSCH transmission in UL subframe 9 (=5+4) (i.e., k=4).

The present embodiment is explained with reference to FIG. 7.

In the step S710, the first cell determines frequency resource ICICinformation (e.g., IOI and/or HII) and time resource ICIC information(e.g., silent subframe pattern) and can transmit the determinedfrequency resource and the time resource ICIC information to the secondcell in the step S720.

In the step S730, the second cell can assume validity of the frequencyresource ICIC information based on the time resource ICIC informationreceived from the first cell. First of all, the second cell can assumeas follows based on the time resource ICIC information.

For instance, if a DL subframe n is configured as a silent subframe,there is no PDCCH transmission in the subframe n. Hence, PUSCHtransmission in a subframe n+k is also not performed. For instance, incase that the first cell configures the DL subframe n as the silentsubframe and informs the second cell of the silent cell, the second cellcan know that the first cell will not perform PUSCH transmission in ULsubframe n+k without any separate information.

And, the second cell can assume validity of the frequency resource ICICinformation (IOI or HII) received together with the time resource ICICinformation as follows. In this case, the IOI or the HII provided to thesecond cell by the first cell has no meaning for the at least ULsubframe n+k. In particular, the IOI of the first cell indicates theextent of UL interference experienced by the first cell on a specificfrequency sub domain and the HII of the first cell indicates stronginterference caused by the first cell on the specific frequency subdomain. Since the first cell does not perform the UL transmission in thesubframe n+k, the IOI or the HII of the first cell becomes theinformation not necessarily to be considered by the second cell in thesubframe n+k.

In the step S730, the IOI is explained in more detail. In case that thesecond cell receives the information indicating that the first cellconfigures a DL subframe n as the silent subframe, it can be assumedthat UL IOI of the first cell is not applied in the subframe n+k. Or,the second cell ignores the IOI value transmitted by the first cell forthe subframe n+k and can override all frequency sub domains in a mannerof setting the IOI value of the first cell to 0 (in particular, the DLinterference experienced by the first cell is low). In other word, it ispossible to say that the second cell considers the UL IOI information ofthe first cell as valid only in the subframe n+k where the subframe n isnot configured as the silent subframe.

According to the method of considering the silent subframe patterntogether with the IOI information in the foregoing description, in caseof the frequency sub domain (or, the frequency sub domain indicatingthat the first cell is experiencing strong UL interference) received thecontent, which indicates that inter-cell interference need to bereduced, via the UL IOI of the first cell, if the first cell configuredthe subframe n as the silent subframe, the second cell can freelyperform a UL scheduling in the subframe n+k regardless of the inter-cellinterference [S740]. By doing this, efficiency of resource utilizationcan be enhanced.

Although the first cell indicates that interference overload is high forthe specific frequency sub domain, if the first cell configures the DLsubframe n as the silent subframe, the first cell can predict that theIOI transmitted to the second cell is not valid in the UL subframe n+k[S750]. In particular, the first cell anticipates that the second cell,which received the UL IOI, may cause strong interference in UL for allfrequency resources in the UL subframe n+k irrespective of the IOI ofthe first cell. By doing so, the first cell can perform UL scheduling ofthe first cell.

Subsequently, an HII case in the step S730 is explained. Similar to theaforementioned IOI, the first cell can transmit HII informationindicating that the first cell causes strong UL interference on aspecific frequency sub domain together with the information indicatingthat the subframe n is configured as the silent subframe to the secondcell. In this case, if the subframe n is configured as the silentsubframe, the second cell can assume that there is no PUSCH transmissionof the first cell in the subframe n+k and the UL HII of the first cellis not applied to the subframe n+k. Or, the second cell ignores the HIIvalue transmitted by the first cell for the subframe n+k and canoverride all frequency sub domains in a manner of setting the HII valueof the first cell to 0 (in particular, the DL interference caused by thefirst cell is low). In other word, it is possible to say that the secondcell considers the UL HII information of the first cell as valid only inthe subframe n+k where the subframe n is not configured as the silentsubframe.

As mentioned in the foregoing description, according to a method ofconsidering both the silent subframe pattern and the HII information, ifthe first cell configures the subframe n as the silent subframe, thesecond cell can freely perform UL scheduling on a frequency sub domainindicated by high interference sensitivity (or, the frequency sub domainwhere the first cell causes strong UL interference) irrespective of theinter-cell interference in the subframe n+k [S740]. By doing so,efficiency of resource utilization can be enhanced.

Although the first cell indicates the extent of the UL interferencecaused by the first cell for the specific frequency sub domain, if thefirst cell configures the DL subframe n as the silent subframe, thefirst cell can predict that the HII transmitted to the second cell isnot valid in the UL subframe n+k [S750]. In particular, the first cellanticipates that the second cell, which received the UL HII, may causestrong interference in UL for all frequency resources in the UL subframen+k irrespective of the HII of the first cell. By doing so, the firstcell can perform UL scheduling of the first cell.

Embodiment 3

The present embodiment explains on resource determination to measureinterference in case that the time resource ICIC information and thefrequency resource ICIC information of one cell are applied together.

An interfering cell can change transmit power in a time domain (e.g.,configuration of a silent subframe pattern) or can change the transmitpower on a frequency domain (e.g., RNTP configuration). If an interferedcell performs interference measurement in a manner of calculating anaverage of the interference of all resource domains without consideringthe transmit power, which varies in time/frequency domain, of theinterfering cell, a result of the interference measurement may representinterference characteristic for a total frequency/time resource. Yet,the result cannot be used for the interference characteristic of aspecific time/frequency resource. Hence, if a delicate interferencecharacteristic for a specific time/frequency resource cannot bedetermined, it becomes difficult to select an appropriate MCS for thecorresponding specific time/frequency resource. For instance, in orderfor a user equipment to properly calculate CSI for a specifictime/frequency resource domain, interference measurement for thecorresponding specific time/frequency resource domain should be properlyperformed.

To this end, it is possible to enable the interference measurement inthe interfered cell to be performed in a manner of limiting to aspecific time/frequency resource domain, which is expected to have anidentical (or similar) interference level. For instance, a userequipment can perform the interference measurement in a manner ofobtaining the average of the interference only in a specifictime/frequency resource domain. To this end, a base station can informthe user equipment of the information capable of determining thetime/frequency resource domain, which is limited for the interferencemeasurement of the user equipment, via an upper layer signaling (e.g.,RRC signaling).

Hence, in case of performing the interference measurement for a limitedresource, the ICIC information (e.g., silent subframe pattern) on thetime resource of the interfering cell and the ICIC information (e.g.,RNTP, IOI, HII) on the frequency resource can be considered together. Inthis case, similar to the aforementioned embodiments, in terms of theinterfered cell, it may be unclear whether the interfering cell performsa silencing in the specific time/frequency resource or a DL transmissionof strong power level.

Hence, in case that the base station informs the user equipment of aresource to perform the interference measurement, it is able to considerthat the RNTP of a corresponding cell has no meaning (in particular, lowinterference is expected on all frequency bands in the silent subframe)in a silent subframe of an interfering cell. For instance, in case thatthe user equipment performs interference measurement limited to aspecific frequency resource, if the interfering cell performs asilencing in a specific subframe while low interference resource isworking with the corresponding specific frequency resource, the userequipment can perform limitless interference measurement for allfrequency domains in the silent subframe of the interfering cell. Tothis end, the base station can inform the user equipment of theinformation on a set of subframes (in particular, the subframe permittedto measure interference for all bands), which correspond to theexception of the interference measurement for the limited frequencyresource, via an upper layer signal.

As mentioned in the foregoing description, in case that the timeresource ICIC information of the interfering cell and the frequencyresource ICIC information are provided at the same time, the interferedcell determines whether the frequency resource ICIC information isapplied based on whether the interfering cell performs a silencing in aspecific subframe, thereby efficiently and properly performing theinterference measurement on the time/frequency resource having identical(or similar) interference characteristic.

Embodiment 4

The present embodiment describes an ICIC operation of each cell in casethat time resource ICIC information of one cell and frequency resourceICIC information of a different cell are exchanged with each other.

FIG. 8 is a flowchart showing an example of the present invention for anICIC operation in case that ICIC information on a time resource of onecell and the ICIC information on a frequency resource of a differentcell are exchanged with each other.

As shown in FIG. 8, a first cell corresponds to a cell determining[S810] and transmitting [S830] the ICIC information (e.g., silentsubframe pattern) on a time resource of the first cell and a second cellcan receive the ICIC information on a time resource of the first cell.And, the second cell corresponds to a cell determining [S820] andtransmitting [S840] the ICIC information (e.g., RNTP, IOI, HII) on afrequency resource and the first cell can receive the ICIC informationon a frequency resource.

Embodiment 4-1

The present embodiment describes an ICIC operation of each cell in casethat the RNTP of the second cell is applied to a silent subframe of thefirst cell.

Assume that the first cell configures a DL subframe n as a silentsubframe [S810] and informs the second cell of the silent subframe[S830]. In this case, the second cell configures a specific frequencysub region as a low DL transmit power region [S820] and can inform thefirst cell of the specific frequency sub region via the RNTP [S840].

In this case, in terms of the second cell, since the DL subframe ncorresponds to a resource where the first cell performs a silencingoperation for all bands, if the second cell also applies a low DLtransmit power to the subframe n on the specific frequency sub domain,which is configured with the RNTP, a corresponding frequency resource ofthe corresponding subframe n cannot be sufficiently used by both thefirst cell and the second cell. In order to solve this sort ofinefficiency, each of the first cell and the second cell can assume thevalidity of the time resource ICIC information of the first cell and thevalidity of the RNTP information of the second cell as follows.

The first cell ignores the RNTP transmitted by the second cell for theDL subframe n, which is configured as the silent subframe by the firstcell, and can assume that the second cell uses high DL transmit power onall frequency bands [S850].

For the DL subframe n, which is configured as the silent subframe by thefirst cell, the second cell can also use the high transmit power on aspecific frequency sub band, which is configured as the low DL transmitpower region according to the RNTP determined by the second cell [S860].

In particular, in the step S850 and S860, both the first cell and thesecond cell can assume that the RNTP of the second cell is not valid inthe subframe, which is configured as the silent subframe by the firstcell. According to the assumption for the RNTP, the operation of eachcell can be defined as follows.

The first cell can inform user equipments belonging to the first cellvia an upper layer signal of a fact that strong interference can occuron all frequency bands in a specific subframe [S870]. Hence, when theuser equipments of the first cell perform measurement on CSI for aspecific frequency sub band or RSRQ (reference signal received quality),if the corresponding specific frequency sub band corresponds to a lowinterference region, the user equipments of the first cell can performthe measurement in a manner of excluding the specific subframe indicatedby the upper layer signal. Or, when the user equipments of the firstcell perform measurement, if the corresponding specific frequency subband corresponds to a high interference region, the user equipments ofthe first cell assume that the measurement for all frequency bands has aproperty identical to the property of the measurement for thecorresponding specific frequency sub band in the specific subframeindicated by the upper layer signal and can perform the measurement viasuch an operation as interpolation and the like.

The second cell can transmit information indicating that high transmitpower will be used for all frequency bands in a specific subframewithout following the RNTP transmitted by the second cell to theneighboring cells except the first cell [S880]. Having received theinformation, the neighboring cells can utilize the information receivedfrom the second cell in case of performing DL scheduling.

Embodiment 4-2

The present embodiment describes an ICIC operation of each cell in casethat the HII of the second cell is applied to a silent frame of thefirst cell.

Referring to FIG. 8 again, the first cell configures a DL subframe n asa silent subframe [S810] and informs the second cell of the silentsubframe [S830]. In this case, the second cell configures a specificfrequency sub region as a low UL transmit power region or a high ULtransmit power region [S820] and can inform the first cell of thespecific frequency sub region via the HII [S840].

In this case, in case that a UL grant for a UL transmission in a ULsubframe n+k is configured as a timing relation transmitted in a DLsubframe n, if the DL subframe n is configured as the silent subframe inthe first cell, it is possible to see that there is no practical ULtransmission of the first cell in the UL subframe n+k. In this case, itis beneficial that the second cell uses high UL transmit power for allfrequency bands in the UL subframe n+k irrespective of the HIItransmitted by the second cell in terms of resource utilizationefficiency. Hence, each of the first and the second cell can assume thevalidity of the time resource ICIC information of the first cell and thevalidity of the HII information of the second cell as follows.

If the DL subframe n is configured as the silent subframe by the firstcell, the first cell ignores the HII transmitted by the second cell forthe UL subframe n+k and can assume that the second cell uses high ULtransmit power on all frequency bands [S850].

If the first cell configures the DL subframe n as the silent subframe,the second cell can also use high UL transmit power on a specificfrequency sub band, which is configured as a low UL transmit powerregion according to the HII determined by the second cell [S860].

In particular, for the subframe n+k where the subframe n is configuredas the silent subframe by the first cell, both the first and the secondcell can assume that the HII is not valid. According to the assumptionfor the HII, the operation of each cell can be defined as follows.

The first cell can perform UL scheduling for the user equipments servedby the first cell in consideration of a point that the HII of the secondcell is not valid in a specific UL subframe (the UL subframe n+k wherethe DL subframe n is configured as the silent subframe) [S870]. In thiscase, if UL grant information, which schedules PUSCH transmission in theUL subframe n+k, cannot be transmitted in the DL subframe n, which isthe silent subframe, multi-subframe scheduling can be used. According tothe multi-subframe scheduling, for instance, the UL grant information,which schedules PUSCH transmission in the UL subframe n+k, can betransmitted not in the DL subframe n but in a different DL subframe(e.g., DL subframe n−1). In this case, the UL grant informationtransmitted in the DL subframe n−1 may include a signaling fieldindicating that the PUSCH transmission scheduled by a corresponding ULgrant is performed in the UL subframe n+k.

The second cell can inform different neighboring cells except the firstcell of information indicating that high transmit power will be used forall frequency bands in a specific subframe without following the HIItransmitted by the second cell. Having received the information, theneighboring cells can utilize the information received from the secondcell in case of performing a UL scheduling

The second cell can transmit information indicating that high transmitpower will be used for all frequency bands in a specific subframewithout following the HII transmitted by the second cell to theneighboring cells except the first cell [S880]. Having received theinformation, the neighboring cells can utilize the information receivedfrom the second cell in case of performing a UL scheduling.

Embodiment 4-3

The present embodiment describes an ICIC operation of each cell in casethat the IOI of the second cell is applied to a silent frame of thefirst cell.

Referring to FIG. 8 again, the first cell configures a DL subframe n asa silent subframe [S810] and informs the second cell of the silentsubframe [S830]. In this case, the second cell determines a specificfrequency sub domain where the second cell is experiencing high level ofinterference [S820] and can inform the first cell of the specificfrequency sub domain via the IOI [S840]. In particular, the second cellcan transmit the IOI to the first cell to make a request for reducingthe level of interference of the first cell on the specific frequencysub domain.

In this case, if the DL subframe n is configured as the silent subframein the first cell, it is possible to see that there is no practical ULtransmission of the first cell in the UL subframe n+k (in this case,assume that there is no application of a multi-subframe schedulingdescribed in the embodiment 4-2). Hence, since the interference from thefirst cell for all frequency bands in the subframe n+k becomes low interms of the second cell, it is able to be assumed that the IOI (orinterference reduction request) of the second cell is automaticallyaccepted in the subframe n+k [S860] and [S880].

Meanwhile, in terms of the first cell, since the UL transmission is notperformed for all frequency bands including the specific frequency subband, which is indicated by the IOI of the second cell as the secondcell is experiencing high UL interference, in the subframe n+k, it isable to automatically obtain a result identical to a result obtainableafter performing an operation according to the interference reductionrequest, without performing a separate ICIC operation according to areception of the IOI of the second cell [S850] and [S870]. In otherword, it is able to assume that the frequency sub bands of which thesecond cell makes a request for interference reduction via the IOI arelimited to the content of the subframe where a UL scheduling isperformed in the subframe, which is not configured as the silentsubframe in the first cell.

Embodiment 5

The present embodiment describes a method of using an additional signalindicating validity of frequency resource ICIC information.

According to the present embodiment, the first cell and the second cellcan exchange an additional signal indicating whether frequency resourceICIC information (e.g., RNTP, HII, and IOI) is valid in a specificsubframe. For instance, the first cell and the second cell can transmita pattern indicating whether the frequency resource ICIC information isvalid (or not valid) in a prescribed subframe in a form of a bitmap. Thesubframe where the frequency resource ICIC information is not valid maycorrespond to a silent subframe.

As a different example, the first cell and the second cell can transmita signal indicating a frequency domain and a subframe where thefrequency resource ICIC information is valid (or not valid). Inparticular, whether the frequency resource ICIC information is valid ina specific subframe and a specific frequency domain can be additionallyindicated while the validity of the frequency domain ICIC information issimply indicated according to a subframe. Specifically, the first celland the second cell can exchange a signal indicating that the frequencyresource ICIC information is valid for all subframes on a specificfrequency domain irrespective of a silent subframe configuration and thesignal indicating that the frequency resource ICIC information is notvalid for a part of the subframe(s) on a different specific frequencydomain.

In this case, the frequency domain where the frequency resource ICICinformation is valid in all subframes may correspond to the frequencydomain used for a signal (e.g., periodical CSI report, SRS transmission,SPS (semi-persistent scheduling) PUSCH transmission) capable of beingtransmitted without a UL dynamic scheduling information received onPDCCH. To this end, the first cell and the second cell can exchangescheduling information (frequency domain assignment information used fortransmitting the corresponding signal) of the signal capable of beingtransmitted without a dynamic scheduling.

Meanwhile, the frequency domain where the frequency resource ICICinformation is not valid in a specific subframe may correspond to thefrequency domain used for a signal capable of being transmitted by theUL dynamic scheduling information received on PDCCH. For instance, thesecond cell can freely schedule UL transmission on the frequency domainin a silent subframe of the first cell. And, if a subframe where a ULgrant is received for a prescribed subframe of the first cellcorresponds to the silent subframe, the second cell can freely performUL transmission on the frequency domain in the corresponding subframe(in particular, if a subframe n corresponds to the silent subframe,subframe n+k).

Embodiment 6

In the aforementioned embodiments, in case that a DL subframe is set toa silent subframe, if a UL grant, which schedules UL transmission in aUL subframe, has a timing relation of which the UL grant is receivedfrom the DL subframe, it is assumed that the corresponding UL subframeimplicitly correspond to the silent subframe as well. In particular,according to the aforementioned embodiments, it assumed a pairingrelation indicating that if a DL subframe n is a silent subframe, a ULsubframe n+k corresponds to the silent subframe as well. Yet, in orderto more flexibly apply a silent subframe configuration, the silentsubframe configuration for a DL silent subframe and a UL silent subframecan be separated. To this end, a bitmap message indicating a UL silentsubframe pattern can be explicitly exchanged between cells via abackhaul link.

Hence, in case that the silent subframe configuration is separatelygiven to a DL and a UL, assumption on whether a frequency resource ICICinformation is valid in a specific subframe and an operation in eachcell can be defined as follows.

First of all, it is explained a case that a DL subframe n of a firstcell is a silent subframe and a UL subframe n+k is not a silentsubframe. This sort of DL-UL subframe relation can be defined in casethat such a scheme mentioned in the first cell as a multi-subframescheduling and the like (e.g., a scheme performing UL transmission inthe UL subframe n+k according to the UL grant received in a DL subframen−1) is applied.

As shown in FIG. 7, in case that the first cell transmits frequencyresource ICIC information (e.g., RNTP, IOI, HII) to the second cell, thesecond cell can assume that the RNTP of the first cell is not valid inthe DL subframe n, which is a silent subframe. Yet, since the ULsubframe n+k is not a silent subframe, the second cell can perform PUSCHscheduling and the like in a manner of assuming that the IOI and the HIIof the first cell are valid.

Meanwhile, as shown in FIG. 8, in case that the second cell transmitsfrequency resource ICIC information to the first cell, the first and thesecond cell ignore the RNTP of the second cell in the DL subframe n,which is the silent subframe and can assume that the second cellperforms DL transmission with higher transmit power in the DL subframen. Meanwhile, since the UL subframe n+k is not a silent subframe, theIOI and the HII of the second cell can be assumed to be valid.

Subsequently, it is explained a case that the DL subframe n of a firstcell is not a silent subframe and the UL subframe n+k is a silentsubframe. In this case, it is possible to see that the first cell doesnot schedule PUSCH transmission in the UL subframe n+k in the DLsubframe n.

As shown in FIG. 7, in case that the first cell transmits frequencyresource ICIC information (e.g., RNTP, IOI, HII) to the second cell,since the DL subframe n is not a silent subframe, the second cell canassume that the RNTP of the first cell is valid. Meanwhile, since the ULsubframe n+k corresponds to a silent subframe, the second cell canassume that the IOI and the HII of the first cell are not valid.

In this case, in terms of the second cell, it can be assumed that thereis no interference from the first cell on all frequency domains of theUL subframe n+k. Hence, the second cell can be used for PUSCHtransmission in the UL subframe n+k. Yet, if a normal DL-UL subframepairing relation is applied to the second cell, the information of thesecond cell scheduling the PUSCH transmission in the subframe n+k istransmitted in the DL subframe n. Since the DL subframe n is thesubframe of which the first cell does not configure it as a silentsubframe, there may exist interference from the first cell. Hence, inorder for the second cell to schedule PUSCH transmission in the ULsubframe n+k in a manner of avoiding the interference from the firstcell, the UL transmission in the UL subframe n+k is needed to bescheduled not in the DL subframe n but in a different DL subframe or theUL transmission in the UL subframe n+k can be scheduled in the DLsubframe n if the interference of the first cell can be avoided. Forinstance, the multi-subframe scheduling scheme (e.g., the schemeperforming PUSCH transmission of the UL subframe n+k according to the ULgrant, which is transmitted in DL subframe n−1) can be applied. Or, thePUSCH transmission in the UL subframe n+k can be scheduled on a newcontrol channel (e.g., e-PDCCH (evolved-PDCCH or enhanced-PDCCH))transmitted in a manner of using a specific resource region (e.g., lowfrequency domain in time domain to which PDSCH of the first cell istransmitted) in the DL subframe n. Or, an operation for minimizing theinfluence of the interference of PDCCH and the like of the first cell ina manner of using PDCCH to which a higher aggregation level compared toa conventional PDCCH is applied can be applied.

Meanwhile, as shown in FIG. 8, in case that the second cell transmitsthe frequency resource ICIC information to the first cell, the first andthe second cell can schedule DL transmission in consideration of an RNTPof the second cell in the DL subframe n, which is not a silent subframe.Meanwhile, since the UL subframe n+k corresponds to a silent subframe,the first and the second cell can operate in a manner of assuming thatthe IOI and the HII of the second cell are not valid.

As mentioned in the foregoing description, for the method of determiningthe validity of the frequency domain ICIC information (e.g., RNTP, IOI,HII) based on the time domain ICIC information (e.g., silent subframepattern) proposed by the present invention, each of the items explainedby the various embodiments of the present invention can be independentlyapplied or two or more embodiments can be implemented in a manner ofbeing simultaneously applied. For clarity, duplicated content isomitted.

FIG. 9 is a diagram for a configuration of a base station deviceaccording to the present invention.

Referring to FIG. 9, the base station device 910 according to thepresent invention can include a transceiving module 911, a processor913, a memory 912, and a plurality of antennas 914. A plurality of theantennas 914 means MIMO transmission and reception supportive of basestation device. The transceiving module 911 can transmit and/or receivevarious signals, data, and information from a different cell and/or auser equipment. The processor 913 can control overall operations of thebase station device 910.

The base station device 910 according to one embodiment of the presentinvention can be configured to perform inter-cell interferencecoordination (ICIC) in a wireless communication system. The base stationdevice 910 depicted in FIG. 9 may correspond to either the base stationdevice of the first cell or the base station device of the second cell.In particular, the first and the second cell may correspond to a sectorof an identical base station or the base station device of the firstcell and the base station device of the second cell may correspond tothe base station device different from each other.

The processor 913 of the base station device of the first cell can beconfigured to transmit time domain ICIC information (e.g., silentsubframe configuration information) of the first cell and frequencydomain ICIC information (e.g., RNTP, UL IOI, UL HII) of the first cellto the second cell via the transceiving module 911. And, the second cellassumes validity of the frequency domain ICIC information based on thetime domain ICIC information of the first cell and operates according tothe validity. The processor 913 of the base station device of the firstcell can be configured to predict a result of the assumption performedby the second cell for the validity of the frequency domain ICICinformation of the first cell. And, the processor 913 of the basestation device of the first cell can be configured to make the firstcell perform UL or DL scheduling based on a prediction result.

Meanwhile, the processor 913 of the second cell can be configured toreceive the time domain ICIC information of the first cell and thefrequency domain ICIC information of the first cell from the first cellvia the transceiving module 911. And, the processor 913 of the basestation device of the second cell can be configured to assume thevalidity of the frequency domain ICIC information of the first cellbased on the time domain ICIC information of the first cell. Theprocessor 913 of the base station device of the second cell can beconfigured to perform UL or DL scheduling of the second cell based on aresult of the assumption.

Besides, the processor of the base station device 910 performs afunction of calculating and processing the information received by thebase station device 910, information to be transmitted to an external,and the like. The memory 912 can store the calculated and processedinformation and the like for a prescribed time and can be replaced bysuch a configuring element as a buffer (not depicted) and the like.

For the aforementioned detail configuration of the base station device,each of the items explained by the various embodiments of the presentinvention can be independently applied or two or more embodiments can beimplemented in a manner of being simultaneously applied. For clarity,duplicated content is omitted

And, in explaining FIG. 9, the explanation on the base station device900 can be identically applied to a relay device as a main agent of DLtransmission or a main agent of UL reception.

Embodiments of the present invention can be implemented using variousmeans. For instance, embodiments of the present invention can beimplemented using hardware, firmware, software and/or any combinationsthereof.

In the implementation by hardware, a method according to each embodimentof the present invention can be implemented by at least one selectedfrom the group consisting of ASICs (application specific integratedcircuits), DSPs (digital signal processors), DSPDs (digital signalprocessing devices), PLDs (programmable logic devices), FPGAs (fieldprogrammable gate arrays), processor, controller, microcontroller,microprocessor and the like.

In case of the implementation by firmware or software, a methodaccording to each embodiment of the present invention can be implementedby modules, procedures, and/or functions for performing theabove-explained functions or operations. Software code is stored in amemory unit and is then drivable by a processor. The memory unit isprovided within or outside the processor to exchange data with theprocessor through the various means known in public.

Detailed explanation on the preferred embodiment of the presentinvention disclosed as mentioned in the foregoing description isprovided for those in the art to implement and execute the presentinvention. While the present invention has been described andillustrated herein with reference to the preferred embodiments thereof,it will be apparent to those skilled in the art that variousmodifications and variations can be made therein without departing fromthe spirit and scope of the invention. For instance, those skilled inthe art can use each component described in the aforementionedembodiments in a manner of combining it with each other. Hence, thepresent invention may be non-limited to the aforementioned embodimentsof the present invention and intends to provide a scope matched withprinciples and new characteristics disclosed in the present invention.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the inventions. Thus, itis intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

INDUSTRIAL APPLICABILITY

The aforementioned embodiments of the present invention can be appliedto various mobile communication systems.

What is claimed is:
 1. A method of performing interference management bya base station (BS) in a wireless communication system, the methodcomprising: receiving, by the BS from another BS, an interferencemanagement message, the interference management message including asilenced subframe pattern of the another BS, an uplink interferenceoverload indication (UL IOI) of the another BS and a bitmap indicatingapplicability of the UL JOT in a time domain; transmitting, to a userequipment (UE), a radio resource configuration (RRC) message includingsubframe set information for interference measurement of the UE; andreceiving, from the UE, channel state information (CSI) feedbackincluding a result of the interference measurement of the UE, whereinthe subframe set information is configured based on the silencedsubframe pattern of the another BS, and wherein the subframe setinformation restricts the interference measurement of the UE to specificsubframes.
 2. The method of claim 1, wherein the subframe setinformation indicates two subframe sets where the interferencemeasurement of the UE is performed separately.
 3. The method of claim 2,wherein the two subframe sets correspond to the silenced subframepattern and a non-silenced subframe pattern respectively.
 4. The methodof claim 1, wherein the silenced subframe pattern indicates subframeswith reduced transmit power or with no transmission.
 5. The method ofclaim 1, wherein the silenced subframe pattern indicates subframes inwhich a predetermined physical channel is not transmitted by the anotherBS or subframes designated by the another BS for interferencecoordination.
 6. The method of claim 5, wherein the predeterminedphysical channel includes a physical downlink shared channel (PDSCH). 7.The method of claim 1, wherein the UL IOI indicates an interferencelevel experienced by the another BS on a frequency domain unit.
 8. Themethod of claim 1, wherein the wireless communication system correspondsto a time division duplex (TDD) system.
 9. A base station (BS)performing interference management in a wireless communication system,the BS comprising: a transceiver; and a processor configured to: controlthe transceiver to receive, from another BS, an interference managementmessage, the interference management message including a silencedsubframe pattern of the another BS, an uplink interference overloadindication (UL IOI) of the another BS and a bitmap indicatingapplicability of the UL IOI in a time domain, transmit, to a userequipment (UE), a radio resource configuration (RRC) message includingsubframe set information for interference measurement of the UE, andreceive, from the UE, channel state information (CSI) feedback includinga result of the interference measurement of the UE, wherein the subframeset information is configured based on the silenced subframe pattern ofthe another BS, and wherein the subframe set information restricts theinterference measurement of the UE to specific subframes.
 10. The BS ofclaim 9, wherein the subframe set information indicates two subframesets where the interference measurement of the UE is performedseparately.
 11. The BS of claim 10, wherein the two subframe setscorrespond to the silenced subframe pattern and a non-silenced subframepattern respectively.
 12. The BS of claim 9, wherein the silencedsubframe pattern indicates subframes with reduced transmit power or withno transmission.
 13. The BS of claim 9, wherein the silenced subframepattern indicates subframes in which a predetermined physical channel isnot transmitted by the another BS or subframes designated by the anotherBS for interference coordination.
 14. The BS of claim 13, wherein thepredetermined physical channel includes a physical downlink sharedchannel (PDSCH).
 15. The BS of claim 9, wherein the UL IOI indicates aninterference level experienced by the another BS on a frequency domainunit.
 16. The BS of claim 9, wherein the wireless communication systemcorresponds to a time division duplex (TDD) system.